This invention relates to the formation of fibers from attenuable material and while the invention is adapted for use in the formation of fibers from a wide variety of attenuable materials, it is particularly suited to the attenuation of various thermoplastic materials, especially mineral materials such as glass and similar compositions which are rendered molten by heating. As with the technique of the prior application Ser. No. 762,789, the present invention may be employed in connection not only with various mineral materials, but also with certain organic materials which are attenuable, such as polystyrene, polypropylene, polycarbonate and polyamides. Since the equipment or apparatus is especially useful in the attenuation of glass and similar thermoplastic materials, the following description refers to the use of glass by way of illustration.
Certain techniques for utilizing whirling currents or tornadoes for the attenuation of molten glass have been disclosed by us in prior applications above identified, such techniques being identified as toration. For example, U.S. Pat. No. 3,885,940, above identified, and also the companion U.S. Pat. No. 3,874,886, disclose development of pairs of counter-rotating tornadoes by directing a gaseous jet into a larger gaseous blast, thereby creating a zone of interaction including pairs of such tornadoes, and into which zone a stream of molten glass is delivered, with resultant attenuation of the glass stream.
In the equipment illustrated in prior U.S. Pat. Nos. 3,885,940 and 3,874,886, the orifice from which the glass stream is delivered to the zone of interaction is located at or adjacent to the boundary of the blast. In our prior application Ser. No. 557,282, now U.S. Pat. 4,015,964, toration arrangements are disclosed in which the glass orifice is positioned in spaced relation to the boundary of the blast, and in which the glass stream is delivered by gravity to the zone of interaction established by the interaction of a jet and a larger blast.
In prior applications Ser. No. 762,789 and 676,755, both the glass orifices and the jet orifices are spaced from the boundary of the blast, and the glass streams are delivered by the action of the jets into zones of interaction of the jets with the blast. In the applications just mentioned, the glass streams are also subjected to two stages of attenuation, one stage occurring in the jet and the other in the blast.
Still further in our application Ser. No. 762,789, the secondary or carrier jet which delivers the glass into the zone of interaction with the blast is caused to develop a stable zone of laminar flow lying between a pair of counter-rotating whirls or tornadoes, and the glass stream is delivered to the laminar zone and thereafter enters the region of the tornadoes of the carrier jet, which latter merge downstream of the carrier jet, but before the carrier jet reaches the principal blast. As is pointed out in our application Ser. No. 762,789, the operation just described results in a two-stage attenuation, the first stage taking place as the glass stream is advanced into the influence of the tornadoes of the carrier jet, and the second stage taking place after the carrier jet and the partially attenuated stream enter the zone of interaction of the carrier jet with the blast.
According to the disclosure of said application Ser. No. 762,789, the zone of laminar flow and the tornadoes of the carrier jet are developed as a result of deflection of individual carrier jets provided for each fiberizing center, such deflection being effected by the use of a guiding or deflecting element which causes the jet to change its path. As is brought out in said application Ser. No. 762,789, such deflection of a carrier jet contributes stability of operation, notwithstanding the delivery of the glass to the carrier jet at a point spaced appreciably from the boundary of the principal blast.
The present invention, in common with application Ser. No. 762,789, has as a major objective, the stabilizing of the stream of glass or other attenuable material by development of a zone of laminar flow between tornadoes established in a jet flow stream. However the jet flow system of the present invention is somewhat different from that of said prior application, but it also provides various of the advantages thereof together with certain other advantages which are distinctive to the technique of the present invention, as is developed hereinafter.
In accordance with the present invention, instead of employing a structural element or means for guiding or deflecting individual carrier jets for each fiberizing center, the carrier jets are arranged in pairs, one pair for each fiberizing center, the jets of each pair being directed along converging axes lying in a common plane to provide for impingement of the jets on each other in said common plane thereof, thereby causing the combined jet flow of each pair of jets to spread laterally toward opposite sides of the common plane of the jet axes. According to the invention, the lateral spreading of the combined jet flow of each pair of jets is limited or obstructed, preferably by positioning the pairs of jets sufficiently close to each other to provide for impingement of the spreading combined jet flow of each pair of jets on the combined jet flow of adjoining pairs of jets. The obstruction of the spreading combined flow of the pairs of jets develops pairs of spaced tornadoes in the jet flow, with zones of laminar flow between the pairs of tornadoes.
In the system of the present invention streams of glass or other attenuable material are fed to the jet flow in the region of the zone of laminar flow from a position in the common plane of the jet axes but offset to one side of both jets. This results in some attenuation of the glass streams, but in the preferred practice of the invention a gaseous blast is directed in a path intercepting the combined jet flow of the pairs of jets, to provide for further attenuation.
Another characteristic of the invention consists of using two jets having approximately the same dimensions for each fiberization center. The kinetic energies of these two jets would preferably be substantially equal.
In the technique of the present invention the tornadoes established in the combined flow of each pair of jets converge downstream of the zone of laminar flow, and the merged jet flow proceeds in a direction to penetrate through the boundary of the principal blast, such penetration creating a zone of interaction also characterized by the generation of a pair of tornadoes according to the toration technique disclosed in the prior U.S. patents fully identified above.
Thus, each stream of glass is subjected to a preliminary gas blast attenuation between the pairs of tornadoes established by the pairs of carrier jets, and the partially attenuated stream is further attentuated in the zone of interaction of the combined carrier jet flow with the principal blast. In this way two-stage attenuation of a single fiber is effected and long fibers are produced without fragmentation.
How the foregoing objects and advantages are obtained, together with others which will occur to those skilled in the art will appear more fully from the following description referring to the accompanying drawings.